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Tau lepton decays with up to two π 0 s in the final state – τ + → π + ν ¯ τ , ρ + ( π + π 0 ) ν ¯ τ , and a 1 + ( π + π 0 π 0 ) ν ¯ τ – are used to study the performance of the barrel region of the silicon-tungsten electromagnetic calorimeter (Si-W ECAL) of the International Large Detector (ILD) at the future e + e - International Linear Collider. Correct reconstruction of the tau decay mode is crucial for constraining the spin state of tau lepton and measuring the Higgs boson CP state in H → τ + τ - decays. We find that about 95 % of π + ν ¯ τ , and 90 % of ρ + ν ¯ τ and a 1 + ν ¯ τ decays produced by the e + e - → Z 0 ∗ → τ + τ - process at an e ± beam energy of 125 GeV are correctly reconstructed. In a smaller ILD detector, with the inner Si-W ECAL radius reduced by about 20 %, these efficiencies are reduced by at most 2 %. The π 0 mass resolution remains below 10 %. Since failures in tau lepton reconstruction are mainly due to photons, an increase of the ILD magnetic field from 3.5 to 4 T does not bring any significant improvement.

Measurements of [Formula omitted] meson production in diffractive deep inelastic scattering [Formula omitted] are presented which are based on HERA data recorded at a centre-of-mass energy [Formula omitted] with an integrated luminosity of 287 pb [Formula omitted]. The reaction [Formula omitted] is studied, where the system X, containing at least one [Formula omitted] meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The kinematics of [Formula omitted] candidates are reconstructed in the [Formula omitted] decay channel. The measured cross sections compare favourably with next-to-leading order QCD predictions, where charm quarks are produced via boson-gluon fusion. The charm quarks are then independently fragmented to the [Formula omitted] mesons. The calculations rely on the collinear factorisation theorem and are based on diffractive parton densities previously obtained by H1 from fits to inclusive diffractive cross sections. The data are further used to determine the diffractive to inclusive [Formula omitted] production ratio in deep inelastic scattering.

Exclusive photoproduction of [Formula omitted] mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction [Formula omitted]. Reactions where the proton stays intact ( [Formula omitted]) are statistically separated from those where the proton dissociates to a low-mass hadronic system ( [Formula omitted]). The double-differential cross sections are measured as a function of the invariant mass [Formula omitted] of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy [Formula omitted]. The phase space restrictions are [Formula omitted], [Formula omitted], and [Formula omitted]. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the [Formula omitted] dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the [Formula omitted] meson mass and width at [Formula omitted] and [Formula omitted], respectively. The model is used to extract the [Formula omitted] contribution to the [Formula omitted] cross sections and measure it as a function of t and [Formula omitted]. In a Regge asymptotic limit in which one Regge trajectory [Formula omitted] dominates, the intercept [Formula omitted] and the slope [Formula omitted] of the t dependence are extracted for the case [Formula omitted].

Signals of QCD instanton-induced processes are searched for in neutral current deep-inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling variable [Formula omitted], the inelasticity [Formula omitted] and the photon virtuality [Formula omitted] GeV [Formula omitted]. The search is performed using H1 data corresponding to an integrated luminosity of 351 pb [Formula omitted]. No evidence for the production of QCD instanton-induced events is observed. Upper limits on the cross section for instanton-induced processes between 1.5 and 6 pb, at [Formula omitted] confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publications, the limits are improved by an order of magnitude and for the first time are challenging predictions.

A first measurement is presented of exclusive photoproduction of [Formula omitted] mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of [Formula omitted] GeV and correspond to an integrated luminosity of 1.16 pb [Formula omitted]. The [Formula omitted] mesons with transverse momenta [Formula omitted] GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, [Formula omitted], are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality [Formula omitted] GeV [Formula omitted], the total energy of the photon-proton system [Formula omitted] GeV and the polar angle of the leading neutron [Formula omitted] mrad. The cross section of the reaction [Formula omitted] is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a [Formula omitted] meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, [Formula omitted], is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction [Formula omitted].

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current ... scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb... and span six orders of magnitude in negative four-momentum-transfer squared, ..., and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in ... An extraction of ... and results on electroweak unification and scaling violations are also presented.

After the Higgs discovery, precise measurements of the Higgs properties and the electroweak observables become vital for the experimental particle physics. A powerful Higgs/Z factory, the Circular Electron Positron Collider (CEPC) is proposed. The Particle Flow oriented detector design is proposed to the CEPC and a Particle Flow algorithm, Arbor is optimized accordingly. We summarize the physics object reconstruction performance of the Particle Flow oriented detector design with Arbor algorithm and conclude that this combination fulfills the physics requirement of CEPC.

A precision measurement of jet cross sections in neutral current deep-inelastic scattering for photon virtualities 5.5 < Q 2 < 80 GeV 2 and inelasticities 0.2 < y < 0.6 is presented, using data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 290 pb - 1 . Double-differential inclusive jet, dijet and trijet cross sections are measured simultaneously and are presented as a function of jet transverse momentum observables and as a function of Q 2 . Jet cross sections normalised to the inclusive neutral current DIS cross section in the respective Q 2 -interval are also determined. Previous results of inclusive jet cross sections in the range 150 < Q 2 < 15 , 000 GeV 2 are extended to low transverse jet momenta 5 < P T jet < 7 GeV . The data are compared to predictions from perturbative QCD in next-to-leading order in the strong coupling, in approximate next-to-next-to-leading order and in full next-to-next-to-leading order. Using also the recently published H1 jet data at high values of Q 2 , the strong coupling constant α s ( M Z ) is determined in next-to-leading order.

The concept of \"particle flow\" has been developed to optimise the jet energy resolution by distinguishing the different jet components. A highly granular calorimeter designed for the particle flow algorithm provides an unprecedented level of detail for the reconstruction of calorimeter showers and enables new approaches to shower analysis. In this paper the measurement and use of the fractal dimension of showers is described. The fractal dimension is a characteristic number that measures the global compactness of the shower. It is highly dependent on the primary particle type and energy. Its application in identifying particles and estimating their energy is described in the context of a calorimeter designed for the International Linear Collider.

The H1 Collaboration reports the first measurement of the 1-jettiness event shape observable τ 1 b in neutral-current deep-inelastic electron-proton scattering (DIS). The observable τ 1 b is equivalent to a thrust observable defined in the Breit frame. The data sample was collected at the HERA ep collider in the years 2003–2007 with center-of-mass energy of s = 319 GeV , corresponding to an integrated luminosity of 351.1  pb - 1 . Triple differential cross sections are provided as a function of τ 1 b , event virtuality Q 2 , and inelasticity y , in the kinematic region Q 2 > 150 GeV 2 . Single differential cross sections are provided as a function of τ 1 b in a limited kinematic range. Double differential cross sections are measured, in contrast, integrated over τ 1 b and represent the inclusive neutral-current DIS cross section measured as a function of Q 2 and y . The data are compared to a variety of predictions and include long-standing and more recent Monte Carlo event generators, predictions in fixed-order perturbative QCD where calculations up to O ( α s 3 ) are available for τ 1 b or inclusive DIS, and resummed predictions at next-to-leading logarithmic accuracy matched to fixed order predictions at O ( α s 2 ) . These comparisons reveal sensitivity of the 1-jettiness observable to QCD parton shower and resummation effects, as well as the modeling of hadronization and fragmentation. Within their range of validity, the fixed-order predictions provide a good description of the data. Monte Carlo event generators are predictive over the full measured range and hence their underlying models and parameters can be constrained by comparing to the presented data.